[2102.08790] Theory and Functionals in the Hypercomplex Kohn-Sham DFT Method
The static/strong correlation error inherent in existing functionals has severely limited the further application of Kohn-Sham (KS) density functional theory (DFT). The recently developed hypercomplex KS (HCKS) theory shows great potential to overcome the fundamental limitations of the conventional KS-DFT, hence further development and application of HCKS will effectively guide the construction of new functionals toward better description of strong correlation. To this end, this work derives the working equations for the HCKS calculation and proves that HCKS using common functionals has much lower computational complexity than reduced density matrix functional theory (RDMFT), while maintaining the same density search space as RDMFT. Moreover, this work combines HCKS with hybrid functionals that are based on orbitals and their occupations. The test on triplet-singlet gaps shows that the systematic error of HCKS due to the lack of static correlation in approximate functionals can be effe
